Based on everything Nasa knows, New Horizons was straight on course for the historic encounter, sweeping within 7,800 miles of the icy world at 31,000mph.

However, official confirmation will not arrive for another 13 hours, because Nasa wants New Horizons to take pictures of Pluto, its jumbo moon Charon and its four smaller moons during this critical time, rather than communicating with Earth.

Nasa marked the moment live on TV, broadcasting from flight operations in Maryland.

The US is now the only nation to visit every single planet in the solar system. Pluto was ninth in the line-up when New Horizons departed Cape Canaveral, Florida, in 2006 to shed light on the mysterious icy world, which was demoted seven months later to dwarf status.

Pluto is one of a number of distant "worldlets" in a region known as the Kuiper Belt.

Its light takes more than four hours to reach the Earth, making communication with New Horizons an exercise in patience.

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